Oil and gas wells can have several strings of casing of differing diameters cemented in the well. Each casing string is usually made up of joints of pipe having threaded ends secured together. A typical casing joint has external threads on its upper and lower ends. A casing collar with internal threads secures the threaded ends together. In larger casing diameters, a casing collar with internal threads may be affixed, such as by welding, to one end of each pipe, the other end having external threads. Normally, the operator relies on the friction of the made-up joint preventing the threaded connectors from loosening while running the string into the well. With larger diameter casing, for example, from 16 inch to 36 inch, the friction of the made-up connector may be inadequate to prevent loosening while running the casing.
Operators have employed anti-rotation keys to prevent loosening. A rectangular pocket or slot is machined on the outer surface of the pin connector. The box connector is machined to include tabs that accept the anti-rotation key. The box connector tab and pin connector pocket will line up after making up the connectors. The workers will then drive a key through the box connector tab and into the pin connector pocket. The key has a slightly greater thickness than the distance from the box connector tab to the innermost wall of the pin connector pocket, resulting in an interference fit. The workers typically will drive the key into place with a hammer. In some casing setups, the key inserts through a threaded hole in the box connector tab and a wrench may be employed to position and secure the key.